When A Unix-Like System Starts Up It Runs Init Nowadays ✓ Solved

When A Unix Like System Starts Up It Runs Init Nowadays This Is A Pr

When a UNIX-like system starts up, it runs init. Nowadays this is a program called systemd on UNIX-like systems. On Mac the similar system manager is called launchd. It runs under PID of 1 and is an ancestor of all other processes. You can see the process with command "ps aux".

If a process is left as an orphan (its parent dies), it gets reassigned as a child of PID 1. These service programs (init, systemd or launchd) are running in the background; on UNIX-like OSs these are commonly referred to as daemons and generally have names ending with the letter “d.” These programs ensure that things start up properly and stay running. If a process crashes systemd (or launchd) can detect this and start it back up.

You will develop a proc_manager program that reads in the commands to execute from an input file one-by-one. You will read one command and its parameters per each line.

Then the proc_manager program will start up the process and "babysit" it. You will run each command in a child process using exec (or one of its variants) and the parent process will wait for each exec to complete. For each child process, there will be log messages written to output and error files, which are named after its index in the sequence of commands read in. For example, process #1 will have logs written to 1.out and 1.err.

Upon start, the string "Starting command INDEX: child PID pid of parent PPID" will be logged to the corresponding output file 1.out. You can retrieve PID and PPID through the return value of fork() or getpid() or getppid(). You can use dup2() to redirect stdout to a file X.out and stderr to X.err.

Note: new executions of a command should append to the previous output and error files, such as 1.out, rather than overwrite them. Timer for each process: you can include the timer.h library and use timer to record the start time of spawning each child process in the parent. Upon finish of an exec (either a successful finish or terminated via a signal), the process should record the finish runtime, and it should write to the output file the string "Finished at FIN, runtime duration DUR" where FIN is the finish time and DUR is the duration of the execution.

Each time a process finishes, the message "Exited with exitcode = X" should be written to the error file of the process. If the process was killed with a signal, then "Killed with signal S" should be written to the error file. S is the signal number that killed the process. This information is gathered using the status parameter of the wait() system call.

If the program cannot be started (exec fails), use perror(" name of command ") to get the error message and command name and write them to the command's error file. Processes that encounter an invalid command (exec fails) should have an exit code of 2.

Remember the exit code of 0 indicates success. Exit codes other than 0 indicate some failure, including a termination via a kill signal.

Sample Paper For Above instruction

In modern UNIX-like operating systems, the init process serves as the foundational process that is launched at boot time and manages the system's overall operation. Traditionally, init was responsible for starting essential services and system daemons, but in contemporary systems, this role has been taken over by processes like systemd on Linux and launchd on macOS, which operate with process ID 1. These processes monitor, restart, and manage other background processes, ensuring system stability and uptime.

Understanding the architecture and functioning of these system managers is crucial for operating system developers and administrators. They foster a resilient environment where processes are automatically restarted upon failure, and system services are orchestrated efficiently. As described in the assignment, creating a process management utility termed proc_manager involves intricate use of UNIX system calls such as fork(), exec(), wait(), and dup2(), enabling parallel process execution and detailed logging for debugging and monitoring.

The core idea behind proc_manager is to read commands from a file, spawn child processes to execute these commands in parallel, and meticulously log their execution details and statuses. Each process's lifecycle—from start, runtime, to termination—is tracked with precise time measurements, and output/error files are maintained for troubleshooting and accountability.

Implementing robust process handling involves several key system calls. The fork() call creates a child process, which then replaces its image with the target command using exec(), ensuring the parent process can monitor and log statuses. Redirecting stdout and stderr to designated log files with dup2() ensures comprehensive recording of process outputs. Timing functions from timer.h facilitate measuring start and finish times, essential for restart logic based on execution duration.

The assignment emphasizes error handling, particularly when exec() fails, necessitating the use of perror() to log the error. It also involves logic to restart processes if they exceed certain runtime thresholds and to handle immediate exits or failures. Processes that terminate swiftly or encounter errors are not restarted, reflecting real-world daemon supervision strategies.

Overall, building this process supervisor as specified enhances understanding of UNIX process control, inter-process communication, and system reliability mechanisms. This project not only underscores the importance of process lifecycle management but also fosters skills in system calls, error handling, and concurrent programming essential for operating system development and system administration.

References

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